The invention relates in general to a testing device for a flow meter installed in a pipeline and delivering pulses proportional to the flow of a measured fluid. The device is of the type which includes a cylinderical calibration container communicating with a by-pass conduit, a switch-over valve for selectively connecting the calibration container in series with the flow meter; a measuring piston arranged for movement in the calibration container and being displaceable by the measured fluid along a measuring path; a signal releasing ring mounted on the measuring piston; a signal generator provided in the wall of the calibration container and cooperating with the signal releasing ring so as to produce a start or stop pulse when the measuring piston reaches a starting or an end position on the measuring part, and means responsive to the start/stop pulse for summing up pulses from the flow meter and comparing the sum with a calibration volume defined by the measuring path.
Testing device of this kind is described for example in the German Utility Model Publication No. 8,229,791. In this known device, a signal generator is installed in the wall of the calibration container at the beginning of the measuring path and another signal generator is provided at the end of the measuring path. One of these signal generators produces a start pulse when the measuring piston together with the signal releasing ring passes a starting position, and the other signal generator produces a stop pulse which initiates the summing up of the electric pulses from the tested flow meter.
In this known testing device it has been found that the starting switch frequently does not have an identical geometrical layout and switching behavior as the stop switch. Consequently, due to the different responding times the measuring accuracy of the testing device is impaired. Moreover, in this known testing device only one measuring cycle can be completed during the passage of the measuring piston through the calibration container.